BBC NEWS
BBCi CATEGORIES   TV   RADIO   COMMUNICATE   WHERE I LIVE   INDEX    SEARCH 

BBC News UK Edition
 You are in: Science/Nature  
News Front Page
World
UK
England
N Ireland
Scotland
Wales
Politics
Business
Entertainment
Science/Nature
Technology
Health
Education
-------------
Talking Point
-------------
Country Profiles
In Depth
-------------
Programmes
-------------
BBC Sport
BBC Weather
CBBC News
SERVICES
-------------
EDITIONS
Wednesday, 25 September, 2002, 20:31 GMT 21:31 UK
Martian 'wobbles' shift climate
Mars, Nasa
Climate clues are locked in the northern cap

Mars undergoes periodic "wobbles" on its axis and variations in its orbit that, like the Earth, may cause it to endure ice ages, say scientists.

The evidence comes from high-resolution images of the planet's northern polar ice cap, a dome of water-ice mixed with dust that is up to 2.5 kilometres (1.5 miles) thick.

Images as well as measurements of the surface profile by the laser altimeter on the Mars Global Surveyor spacecraft reveal a spiral pattern of ice and dust ridges sculpted by fierce winds and evaporation due to sunlight.

The estimated accumulation rate, of 0.05 centimetres (0.02 inches) a year, of these ridges suggest the cap is only about five million years old, and that it was formed at the start of the latest orbital changes that induced the most recent ice age.

Planet-wide ocean

A team led by Jacques Laskar, of France's National Centre for Scientific Research, reports in the journal Nature that Mars experiences dramatic changes in its axis and orbital shape that result in enormous variations in polar "insolation" - the amount of sunlight that falls on the cap.

The same effect happens on the Earth as well, but to a far lesser extent because of the stabilising influence of the Moon's gravity. Mars, however, without a large satellite, can move on its axis up to 47 degrees.

The impact of this can be most easily seen at the north pole.

There, the ice and dust dunes are shaped by the interplay of wind and sunlight. Any variation in solar radiation due to the Sun's changing position in the sky will alter the way the terrain develops.

Dr Laskar's research reveals that the size of the respective layers and the variation in deposition of dust and ice in the past matches Mars' orbital changes.

Drilling missions

The suggestion that the northern cap is only five million years old intrigues astronomers as they calculate that if all the water-ice in the northern cap were melted it would flood the planet with water to a depth of a few metres.

If this happened in the past few million years then it could explain the seemingly freshly cut valleys and erosional features recently identified on the Red Planet.

The answers to such questions will have to wait until man or machine goes to the polar regions.

Commenting on the research, Alan Howard, of the University of Virginia at Charlottesville, US, said: "In the future, missions that land on the planet and drill into the layered deposits may provide definitive interpretations of the climate cycles on Mars."


Mars Odyssey

Future frontiers

Past failures

Talking Point

Forum
See also:

28 May 02 | Science/Nature
28 May 02 | Science/Nature
04 Mar 02 | Science/Nature
23 Sep 02 | Science/Nature
Internet links:


The BBC is not responsible for the content of external internet sites

Links to more Science/Nature stories are at the foot of the page.


E-mail this story to a friend

Links to more Science/Nature stories

© BBC ^^ Back to top

News Front Page | World | UK | England | N Ireland | Scotland | Wales |
Politics | Business | Entertainment | Science/Nature | Technology |
Health | Education | Talking Point | Country Profiles | In Depth |
Programmes